This invention relates to an improved lubricating composition. More particularly, this invention relates to an improved grease composition.
It is, of course, well known, in the prior art, that various lithium soaps can advantageously be used in the preparation of lubricating greases from essentially any lubricating base oil stock, and that the greases thus prepared will, generally, exhibit good grease properties and/or characteristics. It is also well known that certain of these properties and/or characteristics, such as mechanical and/or shear stability, dropping point and oxidation resistance, will vary from grease to grease depending upon the particular lithium soap used therein. For example, greases prepared with a lithium soap derived from a hydroxy-substituted fatty acid such as 12-hydroxystearic acid will generally exhibit better mechanical and/or shear stability and these greases are, generally, obtained in greater yields than those prepared with other lithium soaps. None of the lithium soaps known to be useful in the prior art, when used separately, however, will yield a grease exhibiting the unique combinations of properties, such as a high dropping point, good mechanical and/or shear stability, high resistance to water and good oxidation stability, that are required for greases used in such severe applications as the lubrication of traction motor bearings and the lubrication of wheel bearings on cars with disc brakes, and none offer the long lubricating life generally desired in these applications.
As a result, considerable effort has heretofore been devoted to the preparation of greases comprising mixtures of various lithium salts in an effort to optimize grease properties for a particular application or applications. For the most part, however, this effort has centered around soap combinations comprising at least one lithium soap derived from a hydroxy-substituted fatty acid and particularly 12-hydroxystearic acid, primarily because of the known advantages associated with greases containing these particular soaps and, indeed, several grease compositions comprising one or more such lithium soaps and one or more other lithium soaps and exhibiting particularly desirable combinations of properties have heretofore been developed. Recently, however, the availability and costs of the hydroxy-substituted fatty acids have been subject to severe fluctuations, which have, on occasions, made it difficult to meet the demand for greases exhibiting the unique combination of properties characteristic of greases comprising such fatty acids and nearly impossible to do so on a competitive basis. The need then for a grease composition exhibiting substantially the same high dropping points, the excellent mechanical and shear stability, the high resistance to water, excellent oxidation stability and the long lubricating life which are characteristic of certain greases containing lithium soaps derived from hydroxy-substituted fatty acids, and which can be prepared from a more staple commodity and, generally sold at a lower cost, is then believed to be readily apparent.